Abstract
Nutrient addition to forest ecosystems significantly influences belowground microbial diversity, community structure, and ecosystem functioning. Nitrogen (N) addition in forests is common in China, especially in the southeast region. However, the influence of N addition on belowground soil microbial community diversity in subtropical forests remains unclear. In May 2018, we randomly selected 12 experimental plots in a Pinus taiwanensis forest within the Daiyun Mountain Nature Reserve, Fujian Province, China, and subjected them to N addition treatments for one year. We investigated the responses of the soil microbial communities and identified the major elements that influenced microbial community composition in the experimental plots. The present study included three N treatments, i.e., the control (CT), low N addition (LN, 40 kg N ha-1 yr-1), and high N addition (HN, 80 kg N ha-1 yr-1), and two depths, 0-10 cm (topsoil) and 10-20 cm (subsoil), which were all sampled in the growing season (May) of 2019. Soil microbial diversity and community composition in the topsoil and subsoil were investigated using high-throughput sequencing of bacterial 16S rDNA genes and fungal internal transcribed spacer sequences. According to our results, 1) soil dissolved organic carbon (DOC) significantly decreased after HN addition, and available nitrogen (AN) significantly declined after LN addition, 2) bacterial α-diversity in the subsoil significantly decreased with HN addition, which was affected significantly by the interaction between N addition and soil layer, and 3) soil DOC, rather than pH, was the dominant environmental factor influencing soil bacterial community composition, while AN and MBN were the best predictors of soil fungal community structure dynamics. Moreover, N addition influence both diversity and community composition of soil bacteria more than those of fungi in the subtropical forests. The results of the present study provide further evidence to support shifts in soil microbial community structure in acidic subtropical forests in response to increasing N deposition.
Highlights
Industrialization and urbanization have increased the quantity of nitrogen (N) and phosphorus entering terrestrial systems [1], especially in China’s warm and humid climatic zones [2]
We addressed the following questions in this study: (1) How do bacterial and fungal communities respond to N additions? (2) How do biotic and abiotic elements in the soil modulate the responses of bacterial and fungal communities? (3) What are the potential mechanisms that are responsible for the observed changes in microbial community structure? We hypothesized that N addition could reduce the bacterial and fungal diversity, and, thereby alter soil microbial community composition in subtropical forests
Responses of soil properties and microbial biomass to nitrogen additions Among the soil physicochemical properties we examined, soil pH, soil moisture content (SMC), cation exchange capacity (CEC), soil organic C (SOC), total N (TN), TP, and C:N were not affected by N additions (Table 1)
Summary
Industrialization and urbanization have increased the quantity of nitrogen (N) and phosphorus entering terrestrial systems [1], especially in China’s warm and humid climatic zones [2]. Several meta-analyses have examined the effects of N addition on soil microbial biomass and community composition [19,20,21,22,23,24,25,26,27,28]. N addition reduced soil microbial biomass C (MBC) in temperate forests and grasslands, but significantly increased MBC in tropical/subtropical forests [27]. This increase in microbial biomass following N addition is thought to be mediated by increasing C or N resource availability [28]
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